The download site for pre-compiled binaries, documentation and sources is at SourceForge:
http://sourceforge.net/projects/imtoolkit/files/
Use this link for the latest version: http://sourceforge.net/projects/imtoolkit/files/3.5/
Before downloading any precompiled binaries, you should read before the Tecgraf Library Download Tips.
Some other files are available directly at the IM download folder: